When a cellular wireless mobile communication device is first switched on, its receiver scans an allocated radio frequency (“RF”) spectrum for appropriate signals from base stations in a network that may provide service. Once the cellular wireless mobile communication device has identified and synchronized to a group of base stations, it ranks RF characteristics associated with each of the identified base stations in order of filtered signal strength. The cellular wireless mobile communication device then selects the base station having the strongest filtered signal strength on which to “camp.” Camping on a base station refers to the reading of broadcast information for monitoring paging messages that alert the cellular wireless mobile communication device of an incoming call. Once the cellular wireless mobile communication device camps on a base station, a signaling sequence, referred to as a routing area (“RA”) update, is exchanged between the network and cellular wireless mobile communication device. The RA update informs the network of a subgroup of base stations available in a RA which include the base station on which the cellular wireless mobile communication device is camping. The RA update assists the network in determining how to reach the cellular wireless mobile communication device. For example, when a subscriber number is called, the network must determine how a mobile switching centre (“MSC”) routes a paging message to the cellular wireless mobile communication device.
In a typical cellular system, the cellular wireless mobile communication device does not provide the network with its location information, such as a cell identifier, every time it selects a new cell. Because the radio wave propagation is highly sensitive to changes in the physical environment even in an environment where the RF coverage is very good, cell reselection occurs frequently. Therefore, if the cellular wireless mobile communication device were to inform the network for every cell reselection, signaling between the cellular wireless mobile communication device and network would likely congest the control channels. Further, because signaling messages deliver no revenue to the operator of the network, signaling messages are maintained at a level that is as infrequent as practical. When the MSC receives a call from an outside party who desires to reach the cellular wireless mobile communication device, or its user, the MSC looks up the logical location of the cellular wireless mobile communication device indicated by the RA, and sends a paging message only to a base station controller (“BSC”) in the RA. The BSC then sends paging messages on control channels only to the base station identified in the RA. The cellular wireless mobile communication device then receives the paging message and alerts the user of the incoming call.
Generally, the cellular wireless mobile communication device acts autonomously and simply listens to the broadcast control channels (“BCCH”), which include paging messages, of each cell. However, to provide the location information of the cellular wireless mobile communication device as it travels through the network, the cellular wireless mobile communication device sends an RA update message to the network whenever the cellular wireless mobile communication device crosses an RA boundary. This RA update procedure includes an authentication procedure to verify the cellular wireless mobile communication device as a valid subscriber. If the cellular wireless mobile communication device fails to send a RA update as it leaves one RA and enters into another, the network would send pages to the previous RA, and the cellular wireless mobile communication device would miss incoming calls. If the network fails to receive an RA update from the cellular wireless mobile communication device for some time, such as several hours to several days, the network will detach the cellular wireless mobile communication device from the network. The network may send to voice-mail any received calls for the cellular wireless mobile communication device after detaching. Most cellular systems have a periodic timer that causes the cellular wireless mobile communication device to perform the RA update at a predetermined time interval such as every two hours. An RA update procedure is additionally used when a cellular wireless mobile communication device changes its operating systems, or radio access technology, such as a change between a Global System for Mobile Telecommunication (“GSM”) system and a Universal Mobile Telecommunication Service (“UMTS”) system. The RA update is also performed when the cellular wireless mobile communication device returns to its idle mode from certain communication services such as Dual Transfer Mode (“DTM”).